Compact laser-based near-eye display

ABSTRACT

A near-eye display device comprises a pupil-expansion optic, first and second lasers, a drive circuit coupled operatively to the first and second lasers, a beam combiner, a spatial light modulator (SLM), and a computer. The first and second lasers are configured to emit in respective first and second wavelength bands. The beam combiner is configured to geometrically combine emission from the first and second lasers into a collimated beam. The SLM is configured to receive the collimated beam and to direct the emission in spatially modulated form to the pupil-expansion optic. The computer is configured to parse a digital image, trigger the emission from the first and second lasers by causing the drive circuit to drive current through the first and second lasers, and control the SLM such that the spatially modulated form of the emission projects an optical image corresponding to the digital image.

BACKGROUND

Near-eye display technology has evolved in recent years into an emergingconsumer technology. In head-worn display devices, for example,binocular near-eye display provides 3D stereo vision for virtual-reality(VR) presentation. When implemented with see-through optics, near-eyedisplay provides mixed- or augmented-reality (AR) presentation, where VRelements are admixed into a user's natural field of view. Despite suchbenefits, near-eye display technology still faces various technicalchallenges, including the challenge of providing desired displayluminance using compact, light-weight, low-power components.

SUMMARY

One aspect of this disclosure relates to a near-eye display devicecomprising a pupil-expansion optic, first and second lasers, a drivecircuit coupled operatively to the first and second lasers, a beamcombiner, a spatial light modulator (SLM), and a computer. The first andsecond lasers are configured to emit in respective first and secondwavelength bands. The beam combiner is configured to geometricallycombine emission from the first and second lasers into a collimatedbeam. The SLM has a matrix of electronically controllable pixel elementsand is configured to receive the collimated beam and to direct theemission in spatially modulated form to the pupil-expansion optic.Coupled operatively to the drive circuit and to the SLM, the computer isconfigured to parse a digital image, trigger the emission from the firstand second lasers by causing the drive circuit to drive a first currentthrough the first laser and a second current through the second laser,and control the matrix of pixel elements such that the spatiallymodulated form of the emission projects an optical image correspondingto the digital image.

This Summary is provided to introduce in simplified form a selection ofconcepts that are further described in the Detailed Description. ThisSummary is not intended to identify key features or essential featuresof the claimed subject matter, nor is it intended to be used to limitthe scope of the claimed subject matter. The claimed subject matter isnot limited to implementations that solve any or all disadvantages notedin any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows aspects of an example near-eye display device.

FIG. 2 shows aspects of an example monocular system of a near-eyedisplay device.

FIG. 3 shows aspects of an example edge-emitting diode laser of anear-eye display device.

FIG. 4 shows aspects of an example beam combiner of a near-eye displaydevice.

FIG. 5 shows aspects of an example laser enclosure of a near-eye displaydevice.

FIG. 6 shows aspects of an example display projector of a near-eyedisplay device, based on a reflective LCOS-type SLM.

FIGS. 7A, 7B, and 7C show aspects of example timing diagrams forilluminator modulation in a display projector of a near-eye displaydevice.

FIG. 8 illustrates an example interference fringe that may be observedon a near-eye display device.

FIG. 9 is a plot of a Fourier transform of example laser emissionoverlaid with length ranges corresponding to observed opticalpath-length differences for an example near-eye display device.

FIGS. 10A, 10B, 10C, and 10D are illustrative plots of selected emissionproperties of an example laser as functions of controllable parameters.

FIGS. 11A, 11B, and 11C show aspects of additional example timingdiagrams for laser modulation in a near-eye display device.

FIG. 12 shows aspects of an example near-eye display method.

FIGS. 13A, 13B, 13C, and 13D show aspects of an example pupil-expansionoptic of a near-eye display device.

FIGS. 14A and 14B show aspects of stereoscopic display projection in anexample near-eye display device.

FIG. 15 shows aspects related to ocular sensing in an example near-eyedisplay device.

FIG. 16 shows aspects of an example onboard computer of a near-eyedisplay device.

DETAILED DESCRIPTION

This disclosure is presented by way of example and with reference to thedrawing figures listed above. Components, process steps, and otherelements that may be substantially the same in one or more of thefigures are identified coordinately and described with minimalrepetition. It will be noted, however, that elements identifiedcoordinately may also differ to some degree. It will be further notedthat the figures are schematic and generally not drawn to scale. Rather,the various drawing scales, aspect ratios, and numbers of componentsshown in the figures may be purposely distorted to make certain featuresor relationships easier to see.

As noted above, one challenge facing near-eye display technology is theability to project high-luminance display imagery using compact,light-weight, low-power components. This is especially true for near-eyedisplay devices in which a spatial-light modulator (SLM) is used to formthe display imagery. SLM variants such as liquid-crystal-on-silicon(LCOS) and digital micromirror device (DMD) matrices are capable ofhigh-brightness operation with good spatial and color fidelity. Theoverall power efficiency of an SLM-based display is limited, however, bythe efficiency of illumination of the SLM. Light-emitting diode (LED)emitters, while sufficiently compact for near-eye display, exhibitsignificant etendue loss and require downstream polarization filteringfor SLM illumination. Etendue and polarization losses for LEDillumination of an SLM may be about 30% and 50%, respectively.

In contrast, the output of a semiconductor laser is intrinsicallypolarized and etendue-conserving, and some semiconductor lasers providehigh brightness and high efficiency. Nevertheless, the spatial andtemporal coherence of laser emission may be problematic for near-eyedisplay. At any angle in the user's field of view, a near-eye displaydevice admits of plural optical paths from the emission source to theuser's anatomical pupil. When coherent light arriving along any two ofthe optical paths converges at the pupil, such light will interfereconstructively or destructively. Accordingly, at angles in thefield-of-view where the difference in the optical path lengths matches alongitudinal mode of the coherent emission, the user may see adistracting display artifact in the form of an interference fringe.

The solutions herein provide practical ways of using laser emission toilluminate an SLM in a near-eye display device. Among other advantages,they provide high brightness with fewer artifacts of illuminationcoherence. In this manner, the disclosed solutions, enacted separatelyor in any combination, enable compact, light-weight, energy-efficientnear-eye display.

One solution is to illuminate the SLM using plural lasers in one to allof the primary-color channels. The plural lasers of each primary-colorchannel may differ in cavity length, thereby providing broader (i.e.,less monochromatic) emission, with additional longitudinal modes. Thus,for any mode matched to an optical path-length difference and causing aninterference fringe, there will be one or more additional modesunmatched to the optical path-length difference. As a result,interference fringes due to any one mode are effectively ‘washedout’—i.e., reduced to a chromatic variation that the user cannotperceive, thus mitigating potentially distracting visual artifacts.

Another solution achieves a similar effect but with fewer lasers foreach primary-color channel. It leverages the broadened gain spectrum ofa semiconductor laser driven by modulated current of sufficienthigh-frequency content. By modulating the drive current above and belowthe lasing threshold over predetermined intervals, stimulated emissionis achieved over a range of wavelengths (and longitudinal modes) broadenough to wash out the interference fringes as noted above. In someexamples, a single drive-modulated laser can simulate the emissionspectrum of plural lasers having different cavity lengths.

Related to the strategies above is an additional solution of combining,efficiently and compactly, the output of plural semiconductor lasers.State-of-the-art birefringence- or diffraction-based beam combiners maynot be scalable to larger numbers of combined beams without exceedingthe tight dimensional constraints of a practical near-eye displaydevice. By contrast, the geometric beam combiner disclosed herein islinearly scalable to larger numbers of combined beams. Furthermore, thearrangement of the geometric beam combiner relative to the individuallasers allows the same set of collimation optics to be used to collimatethe emission from every beam en route to the SLM.

Turning now to the drawings, FIG. 1 shows aspects of an example near-eyedisplay device 10. The near-eye display device is configured to be wornand operated by a user and to display still or moving images in theuser's field-of-view. In some examples, the near-eye display device mayinclude or be part of an AR or VR system that presentscomputer-generated, holographic imagery in the user's field-of-view. Insome examples, user-input componentry of the AR or VR system may enablethe user to interact with (e.g., manipulate) such imagery. To supportany, some, or all of these functions, inter alia, near-eye displaydevice 10 includes an onboard computer 12 having a processor 14 andassociated computer memory 16. In the illustrated example, near-eyedisplay device 10 takes the form of a head-mounted visor. In otherexamples, a near-eye display device may take the form of goggles, ahelmet, or eyeglasses. In still other examples, a near-eye displaydevice may be a component of a non-wearable display system, such as adisplay system installed in a vehicle.

Near-eye display device 10 is configured for binocular image display. Tothat end, the near-eye display device includes a right monocular system18R that presents a right optical image 20R in front of the user's righteye, and a left monocular system 18L that presents a left optical image20L in front the user's left eye. For stereoscopic display the right andleft optical images may be configured with stereo disparity appropriateto display a three-dimensional subject or scene (as described withreference to FIGS. 14A and 14B). In other examples, binocular displaymay be provided via a single display projected system akin monocularsystem 18, but configured to project the right and left optical imagesinto the right and left eyes, respectively.

FIG. 2 shows aspects of an example monocular system 18 of near-eyedisplay device 10. The monocular system includes a display projector 22configured to form an optical image 20. The display projector includes ahigh-resolution SLM 24 illuminated by a plurality of lasers 26. Eachlaser is configured to emit (i.e., lase) in a particular wavelengthband—e.g., first laser 26A is configured to emit in a first wavelengthband, second laser 26B is configured to emit in a second wavelengthband, and third laser 26C is configured to emit in a third wavelengthband. In some examples, the plurality of lasers may include at least onelaser of each primary color—e.g., red, green, and blue.

The primary color red refers herein to light of one or more bands,however narrow, that fall within a range of 625 to 700 nanometers (nm).The primary color green refers to light of one or more bands, howevernarrow, that fall within a range of 500 to 565 nm. The primary colorblue refers to light of one or more bands, however narrow, that fallwithin a range of 440 to 485 nm. In some examples, the wavelength rangesof the primary colors here noted may be broadened by as much as 10%. Insome examples, the ranges of the primary colors here noted may benarrowed by as much as 10%.

Any, some, or all of the lasers may take the form of a semiconductorlaser, such as a diode laser. In more particular examples, any, some, orall of the lasers may take the form of an edge-emitting diode laser, adouble-heterostructure laser, a quantum-well laser, a distributedBragg-reflector laser, a vertical-cavity surface-emitting laser, and/oran external-cavity laser, as examples. Efficient, compact lasers ofvirtually any architecture may be used.

FIG. 3 shows aspects of an example edge-emitting diode laser 26A. Laser26A includes an elongate optical cavity 28 spanning a gain structure 30and a reflector structure 32. The gain structure includes epitaxiallayers 34P and 34N, which bracket the optical cavity in the epitaxialdirection. Epitaxial layer 34N is an n-doped layer grown on n-typesubstrate 36 and coupled to electrically conductive (e.g., metal)cathode 38. Epitaxial layer 34P is a p-doped layer grown on epitaxiallayer 34N and coupled to electrically conductive anode 40. Partiallyreflective aperture 42 is arranged at one end of the optical cavity;reflector structure 32 is arranged at the opposite end. Pumped byelectric current flowing from anode 40 to cathode 38, gain structure 30amplifies the light reflecting back and forth within the optical cavityvia stimulated radiative emission. Reflector structure 32 may comprise adiffractive reflector providing high reflectance and wavelengthselectivity. In one example, the reflector structure includes a coatedfacet of the diode laser with parallel layers of alternating refractiveindex aligned perpendicular to the optical cavity. Reflections from theinterfaces between layers combine constructively to achieve a partiallyor highly reflective facet in a selected wavelength band.

Continuing in FIG. 3 , the emission from an edge-emitting diode laserdiverges maximally in a wide-divergence plane 44W and diverges minimallyin a narrow-divergence plane 44N, orthogonal to the wide-divergenceplane. In some examples, the ‘angle’ of divergence in thewide-divergence plane may be diffraction-limited and Gaussian, at 20 to40 degrees FWHM; the angle of divergence in the narrow-divergence planemay be about 5 to 10 degrees.

Each laser 26 of display projector 22 is coupled operatively to drivecircuit 48. The drive circuit is configured to drive a controlledcurrent through each of the lasers—a first current through first laser26A, a second current through second laser 26B, etc. More particularly,the controlled current is driven through gain structure 30, from anode40 to cathode 38. In some examples, drive circuit 48 is configured todrive a periodic current through the gain structure. This featuresupports field-sequential color display, pulse-width modulation forcolor balance, and spectral broadening as described hereinafter. Thedrive circuit may include, inter alia, a pulse-width modulator and atransconductance amplifier for each driven laser.

In some examples, the plurality of lasers 26 may illuminate SLM 24 via abeam combiner arranged in display projector 22. The beam combiner may beconfigured to geometrically combine concurrent and/or sequentialemission from each of the lasers into a collimated beam. FIG. 4 showsaspects of an example beam combiner 50A. Beam combiner 50A includes alaser enclosure 52 in which lasers 26 are arranged. FIG. 5 shows aspectsof an example laser enclosure 52A.

Laser enclosure 52A includes a window 54 configured to transmit theemission from the lasers. In some examples, the atmosphere within thelaser enclosure may be substantially depleted of oxygen. Each of thelasers 26 may be oriented in laser enclosure 54A such that thewide-divergence planes 44W of the lasers are parallel to each other andorthogonal to base 56 of the laser enclosure. To that end, the lasersmay be oriented with mutually parallel optical cavities 28. In someexamples, some or all of the lasers may share an electrode, such ascathode 38, which is arranged in contact with base 56. In theillustrated example, the base delimits a flat mount 58 configured tocarry heat away from the lasers. While not strictly necessary, any,some, or all of the lasers 26 may be arranged such thatnarrow-divergence plane 44N is common to all of the lasers. To that end,the lasers may be arranged such that every optical cavity 28 lies withinthe same narrow-divergence plane.

Generally speaking, the laser enclosure may be configured to redirect(viz., to reflect or refract) the emission from any, some, or all of thelasers out of the narrow-divergence plane. This beam-turning effectcontributes to an overall compact configuration of the beam combiner. Inthe illustrated example, laser enclosure 52A includes a mirror 60configured to receive and reflect emission from lasers 26 and therebyachieve this effect. In the illustrated example, mirror 60 is arrangedwithin the laser enclosure, behind window 54. In some examples themirror may support one or more high-reflectance coatings—e.g., adifferent diffractive coating for each primary color, configured toreflect wavelengths corresponding to that primary color. In someexamples, the mirror 60 may be a glass mirror. In other examples, themirror may comprise highly polished and passivated metal, such asaluminum.

As shown in FIG. 4 , the beam combiner may include one or morecollimation optics configured to collimate the combined emission fromthe lasers. In the illustrated example, beam combiner 50A includes awide-diameter cylindrical collimation optic 62W and a narrow-diametercylindrical collimation optic 62N. The wide-diameter cylindricalcollimation optic has a cylindrical axis 64W aligned normal to thewide-divergence planes of the lasers. The narrow-diameter cylindricalcollimation optic has a cylindrical axis 64N aligned normal to any planeorthogonal to the wide-divergence planes of the lasers. Accordingly, thewide-diameter cylindrical collimation optic reverses the divergenceoccurring in wide-divergence planes 44W, and the narrow-diametercylindrical collimation optic reverses the divergence occurring innarrow-divergence planes 44N. In other examples, an engineeredaspherical Fresnel optic may be used to collimate the combined emissionfrom lasers 26. Turning optics 66A and 66B of beam combiner 50A fold theoptical axis of laser enclosure 52, contributing to an overall compactconfiguration. Beam combiner 50A includes one or more sensors 68 (e.g.,photodiodes) having an output responsive to the concurrent emission oflasers 26. Output of the sensor can be used to maintain color balance inmonocular system 18, as described further below.

Beam combiner 50A includes a diffuser 70 arranged in series with the oneor more collimation optics and configured to diffuse the emission fromlasers 26. The diffuser is configured to homogenize the collimated beamso that the emission from each laser homogeneously illuminates thematrix of pixel elements of SLM 24. Beam combiner 50 includes a laserdespeckler 72 arranged in series with the collimation optics andconfigured to despeckle the emission from lasers 26. ‘Speckle’ isobserved when a spatially coherent, monochromatic wavefront interactswith a surface rough enough to scatter the light along optical pathsthat differ on the order of a wavelength and arrive at the sameobservation point. In the illustrated example, the diffuser is arrangedoptically downstream of the collimation optics, and the despeckler isarranged optically downstream of the diffuser.

A beam combiner may be configured to geometrically combine emission fromplural lasers 26 irrespective of the wavelength or polarization state ofthe emission. For instance, a beam combiner may combine emission fromfirst and second lasers having the same emission spectrum but differingsubstantially in output power. A first laser of higher output power maybe turned when high brightness is required in a given color channel; asecond laser of lower output power may be turned on when high-brightnessis not required. A beam combiner may also combine emission from lasershaving different emission spectra, as described hereinafter.

SLM 24 of FIG. 2 includes a matrix of electronically and independentlycontrollable pixel elements. The particular SLM technology may vary fromone implementation to the next. In FIG. 2 , display projector 22 formsoptical image 20 by reflection of laser emission from the SLM. In otherexamples, an optical image may be formed by transmission of the laseremission through a suitably configured, transmissive SLM. In someexamples, the SLM may comprise a liquid-crystal-on-silicon (LCOS)matrix. In other examples, the SLM may comprise a digital lightprojector (DLP) such as a digital micromirror device (DMD).

FIG. 6 shows aspects of an example display projector 22A of a near-eyedisplay device. Display projector 22A is based on a reflective LCOS-typeSLM 24A. The display projector includes a PCB mounting 74. Arranged overthe PCB mounting, CMOS layer 76 defines the matrix of pixel elements ofthe SLM. A high-efficiency reflective coating 78 is arranged over theCMOS layer and configured to reflect the incident beam from beamcombiner 50. The incident beam is spatially modulated via liquid-crystal(LC) layer 80. The LC layer includes a film of LC molecules (e.g.,nematic LC molecules) maintained in quiescent alignment via alignmentlayer 82. One or more transparent electrodes 84 are arranged over thealignment layer. The one or more transparent electrodes may include adegenerately doped semiconductor (e.g., indium tin oxide) on a suitablesubstrate. In other examples, the one or more transparent electrodes mayinclude a microwire mesh or an extremely thin metal film. Cover glass 86is arranged over the one or more transparent electrodes. In thisconfiguration, the spatially modulated light reflecting from reflectivecoating 78 is directed back through the stack to exit polarizer 88 andthen on to the eyepiece (e.g., pupil-expansion optic) of monocularsystem 18.

Computer 12 is coupled operatively to drive circuit 48 and to SLM 24.The computer is configured to parse a digital image, which may compriseplural component images, each associated with a corresponding primarycolor (e.g., red, green, and blue). The computer is configured totrigger emission from any, some, or all of the lasers 26 by controllingthe drive currents supplied to gain structures 30 of the lasers by drivecircuit 48. The computer is also configured to control the matrix ofpixel elements of SLM 24. Such control is enacted synchronously andcoordinately, such that the spatially modulated form of the emissionemerging from the SLM projects an optical image 20 corresponding to theparsed digital image. In some examples, the computer is configured tocoordinately control the drive circuit and the matrix of pixel elementsin a time-multiplexed manner to provide field-sequential color display.By repeating such control over a time-indexed sequence of digitalimages, the computer may cause display projector 22 to project video.

Returning again to FIG. 2 , display projector 22 projects optical image20 through a physical aperture of finite size. Optics downstream of thedisplay projector focus the optical image onto the anatomical right orleft pupil of the user. In doing so, the downstream optics direct theimage through an entry pupil, defined as the image of the physicalaperture at the anatomical-pupil position. Due to the small size of thephysical aperture and other factors, the entry pupil may be too small toalign reliably to the user's anatomical pupil. Accordingly, monocularsystem 18 includes a pupil-expansion optic 90. In the illustratedexample, SLM 24 is configured to direct the combined emission fromlasers 26, in spatially modulated form, to the pupil-expansion optic.The pupil-expansion optic releases the optical image over an expandedexit pupil, which may be large enough to cover the entire area overwhich the user's pupil is likely to be. Such an area is called an‘eyebox’.

Pupil-expansion optic 90 is configured to receive optical image 20 fromdisplay projector 22 and to release an expanded form 20′ of the opticalimage toward the pupil position 92. In the illustrated example, thepupil-expansion optic includes an optical waveguide 94, an entry grating96 and an exit grating 98. The pupil-expansion optic may also includeother gratings not shown in FIG. 2 . It will be understood that the term‘grating’ is broadened herein to include any kind of diffractive opticalelement (DOE), irrespective of whether that element includes a patternof elongate diffractive features. Non-limiting example gratings includea surface-relief type grating comprising a series of closely spacedchannels formed on the optical waveguide, or a volume grating orindex-modulated grating formed in the optical-waveguide material.

Entry grating 96 is a diffractive structure configured to receiveoptical image 20 and to couple the light of the optical image intooptical waveguide 94. After coupling into the optical waveguide, thedisplay light propagates through the optical waveguide by total internalreflection (TIR) from the front and back faces of the optical waveguide.Exit grating 98 is a diffractive structure configured to controllablyrelease the propagating display light from the optical waveguide in thedirection of pupil position 92. To that end, the exit grating includes aseries of light-extraction features arranged from weak to strong in thedirection of display-light propagation through the optical waveguide, sothat the display light is released at uniform intensity over the lengthof the exit grating. In this manner, pupil-expansion optic 90 may beconfigured to expand the exit pupil of display projector 22 so as tofill or overfill the eyebox of the user. This condition providesdesirable image quality and user comfort.

In some examples, pupil-expansion optic 90 may expand the exit pupil ofdisplay projector 22 in one direction only—e.g., the horizontaldirection, in which the most significant eye movement occurs. Here, thedisplay projector itself may offer a large enough exit pupil—natively,or by way of a vertical pre-expansion stage—so that vertical expansionwithin the optical waveguide is not necessary. In other examples,pupil-expansion optic 90 may be configured to expand the exit pupil inthe horizontal and vertical directions. In such examples, display lightpropagating in a first direction within the optical waveguide mayencounter a turning grating (not shown in FIG. 2 ) having a plurality ofdiffraction features arranged weak to strong in a first direction. Theturning grating may be configured such that the light diffracted by thediffraction features is turned so as to propagate in a second direction,having now been expanded in the first direction. Parallel rays of theexpanded light then encounter exit grating 98 and are out-coupled fromthe waveguide as described above. A more detailed example of apupil-expansion optic employing a turning grating is describedhereinafter, in connection to FIGS. 13A through 13D.

Despite the utility of diffractive optical elements for coupling lightinto and out of an optical waveguide, in-coupling and out-couplingoptical elements based on reflection, refraction, and/or scattering areenvisaged as alternatives to DOEs. In still other examples, apupil-expansion optic may include, in lieu of an optical waveguide, aseries of reflective-refractive interfaces (so-called ‘venetian blinds’)oriented 45 degrees relative to the optical axis. Irrespective of theparticular pupil-expansion technology employed, a pupil expansion opticnecessarily increases the number of optical path lengths between theemission source and the user's pupil, thereby increasing the potentialfor overlap between the optical path lengths and the longitudinal modespacings of coherent laser emission.

FIGS. 7A, 7B, and 7C show aspects of example timing diagrams forilluminator modulation in a display projector of a near-eye displaydevice. The timing diagram of FIG. 7A illustrates the strategy known as‘field-sequential color display’, where red, green, and blueilluminators are energized during successive intervals within each imageframe. During the interval in which the red-emitting illuminator isenergized, the pixel elements of the SLM are biased according to thecomponent digital image corresponding to the red-color channel, andlikewise for the green- and blue-emitting illuminators. The requiredmodulation for field-sequential color display is slow on the timescaleof illuminator and SLM response but fast on the timescale of the humanocular system. Accordingly, the component red, green, and blue imagesappear fused to the near-eye display user.

For each timing diagram in FIG. 7A, ff., the vertical axis representsdrive current applied to the red-, green-, or blue-emitting illuminator.In examples in which the illuminator is a laser, the modulation isbetween below-threshold drive current A and above-threshold drivecurrent B, where ‘threshold’ refers to the laser's drive-currentthreshold for stimulated radiative emission. In some examples, a nonzerovalue of below-threshold drive current A provides decreased power lossand emission latency.

The insets in FIGS. 7A, ff are plots of emission power as functions ofwavelength. The wavelength range for each inset well within and muchnarrower than the afore-noted wavelength range of the indicated primarycolor. The inset of FIG. 7A shows an example emission spectrum 102G1 ofgreen-emitting diode laser 26G1, using the indicated modulation scheme.The emission spectrum has a relatively narrow FWHM₁, which correspondsto a sparse longitudinal-mode spacing. FIG. 8 provides a roughillustration of a display artifact 104 that may be observed through anear-eye display device in which an SLM is illuminated by laser 26G1. Asnoted hereinabove, the source of the artifact is coincidence between alongitudinal mode of coherent emission and the path-length differencealong plural optical paths that carry the coherent emission from thelaser to the user's pupil.

FIG. 9 presents data that illustrates this coincidence by way of anon-limiting, example. In particular, FIG. 9 is a plot of a Fouriertransform 106 of green laser emission, such as the emission from laser26G1, overlaid with plural length ranges 108. The length rangescorresponding to selected optical path-length differences observable foran example near-eye display device. As expected, the longitudinal modespacing is approximately two times the optical cavity length (which isthe cavity length multiplied by the index of refraction) of the laser.For instance, a blue laser may have a cavity length in the range of 300to 900 μm; a green laser may have a cavity length in the range of 400 to1000 μm; and a red laser may have a cavity length in the range of 600 to2000 μm.

More particularly, length range 108A corresponds to complex 1a DOE1 1a31b 1b 01b33 RG plate. Length range 108B corresponds to complex 1a DOE11a3 1b1b 01b33 BG plate. Length range 108C corresponds to zero-order inglass RG plate. Length range 108D corresponds to complex 1b DOE101b31a1a1a33 RG plate. Length range 108E corresponds to complex1bDOE101b31a1a1a33 BG plate. Length range 108F corresponds toDOE3-2order RG plate. Length range 108G corresponds to DOE2 order BGplate. Because Fourier transform 106 has peak coherence within lengthrange 108G, it is expected that this mode will give rise to aninterference fringe due to an optical path length passing through the RGplate at second order.

While coherent illumination may cause display artifacts in displaysystems of various kinds, a near-eye display device with apupil-expansion optic is particularly prone to such artifacts—as theprimary function of the pupil expander is to multiply the number ofoptical paths from the display projector to the user's pupil. Presentednext are various spectral-broadening approaches that may be used in anear-eye display device to wash out the interference fringes caused bythe coincidence between longitudinal modes and optical path-lengthdifferences.

In some examples, a portion of the overall fringe-reduction strategy mayinclude avoidance of longitudinal modes that yield the strongestinterference fringes for a given near-eye display configuration. Thus,in a near-eye display device that admits of a plurality of optical pathlengths from a laser and through a pupil-expansion optic, where thecavity length of the laser corresponds to a longitudinal mode spacing,the cavity length may be selected to avoid coincidence between thelongitudinal mode spacing and any difference in the plurality of opticalpath lengths. That approach may be practical only for avoidance of themost prominent and/or predictable interference fringes. Accordingly, inscenarios where coincidence between a longitudinal mode of a first laserand an optical path-length difference gives rise to an interferencefringe, the cavity length of a second laser of the same primary colormay be selected to wash out the interference fringe. The term ‘wash out’is meant to convey the idea that every combination of optical pathscarrying a longitudinal mode that coincides with the path-lengthdifference also carries numerous other longitudinal modes that fail tocoincide with the path-length difference. Each of the other modescombines to weaken the brightness contrast of the interference fringe,reducing it to a chromatic variation that the user cannot perceive.

Thus, one approach herein is to provide spectral diversity by including,within each primary-color band, emission from plural lasers with offsetemission-wavelength bands. Returning briefly to FIG. 5 , laser enclosure52A includes two lasers of each primary color: red-emitting lasers 26R1and 26R2, green-emitting lasers 26G1 and 26G2, and blue-emitting lasers26B1 and 26B2. The inset of FIG. 7B represents a first wavelength band102G1 for green-emitting laser 26G1 and a second wavelength band 102G2for green-emitting laser 26G2. The second wavelength band is spectrallydistinct from the first wavelength band but of the same primary color(green) as the first wavelength band. The plot also shows, in dashedlines, the combined emission profile from both of the green-emittinglasers at equal power. The combined emission profile has a FWHM₁₊₂,which is greater than the FWHM of wavelength band 102G1 and greater thanthe FWHM of 102G2.

In some examples the peak wavelength of the first wavelength band mayexceed the peak wavelength of the second wavelength band by threenanometers or more. More generally, the first and second wavelengthbands (and so on) may be selected to provide spectral diversity forfringe mitigation, while still providing desired irradiance in the sameprimary-color channel. As illustrated in FIG. 10A, the peak emissionwavelength of a diode laser may increase with increasing cavity length.Accordingly, desired wavelength diversity may result from the combinedemission of a first laser 26G1 and a second laser 26G2, which differsubstantially in cavity length. In other words, the cavity lengths maydiffer in accordance with an engineering specification, not merely as aresult of manufacturing tolerance. In some examples, the cavity lengthof the first laser may exceed the cavity length of the second laser byfive percent or more.

The examples above should not be construed to limit the range ofvariants and alternatives for achieving the desired spectral broadening.The principles illustrated in the drawings for green laser emissionapply equally to laser emission of any primary or non-primary color.While FIG. 5 shows two lasers of each primary color, a givenprimary-color channel may include more than two lasers, or only one. Inany configuration, if spectral diversity sufficient to wash out the redinterference fringes cannot be provided by two red-emitting lasers, thena third red-emitting laser may be added. If the interference fringesfrom one, suitably configured blue-emitting laser are acceptably subtle,then a second blue-emitting laser may be unnecessary. The foregoingconfigurations enable concurrent operation of selected combinations oflasers. That approach may provide maximum display brightness and asimplified control strategy. Nevertheless, another acceptable approachis to operate the indicated combination of lasers in a time-multiplexedmanner and to rely on the latency of the human ocular system to fusesuccessive fringe-prone image subframes into a fringe-averaged result.This variant is shown in the timing diagram of FIG. 7C.

As noted hereinabove, any, some, or all of the lasers 26 may include areflector structure 32 comprising an electrooptical material. By varyingthe control voltage applied to the reflector structure, the gainspectrum of the laser may be shifted such that the emission-wavelengthband of the laser is controllable based on the control voltage. FIG. 10Bprovides illustrative plot showing an example dependence of peakemission wavelength on control voltage. In examples supporting thisvariant, drive circuit 48 may be further configured to vary the controlvoltage based on control signal from the computer, in order to urge theemission-wavelength band toward a predetermined wavelength distribution.This feature can be used to simulate a variable cavity length.Controlled variation of the gain spectrum may be used, for example, toquell fringes that appear under particular operating conditions of anear-eye display device, such as when the user's gaze is directed toangles at the extrema of the field-of-view.

Another way of achieving spectral diversity is to leverage the effect ofdrive-current transients on the gain spectrum of a semiconductor laser.This tactic may require fewer lasers to achieve a similar effect as themulti-laser configurations above. For some lasers, a drive-currentexcursion above the lasing threshold triggers stimulated emission over arelatively broad range of wavelengths (and longitudinal modes). Withcontinued above-threshold bias, the emission relaxes to a narrowerdistribution at the long-wavelength end of the range. By modulating thedrive current above and below the lasing threshold over narrow enoughintervals, the relaxation stops abruptly. Thus, under steady-stateperiodic modulation with sufficient high-frequency content, thesteady-state emission from the laser is broadened (FIG. 10C) andblue-shifted (FIG. 10D) relative to the emission under direct-current(d.c.) bias.

In view of this effect, drive circuit 48 may be configured to drive aperiodic current through the gain structure of any laser 26. Computer 12may be configured to control the periodic current to drive plural cyclesof modulation through the gain structure during projection of a singleoptical image (e.g., a primary-color component of a digital image). As aresult the wavelength band of the emission from the laser may be broaderthan the wavelength band of emission from the same laser when driven byunmodulated drive current. In some examples the periodic currentincludes a pulse-modulated current including a train of current pulses.As noted above, the value of the pulse width may influence the gainprofile of the laser over a domain of sufficiently short pulse widths.The plot in FIG. 10C provides an illustration of this effect. In moreparticular examples, the pulse-modulated current may include a train ofcurrent pulses having a pulse width of twenty nanoseconds or shorter.

The timing diagram of FIG. 11A shows an example pulse train for laser26G1. The inset of FIG. 11A shows an emission-wavelength band broadenedwith respect to the emission-wavelength band of the same laser, shown inFIG. 7B. FIG. 11B shows train of shorter pulses for the same laser, andthe inset illustrates the emission-wavelength band further broadened.

As noted hereinabove in the context of cavity-length variation, aportion of the fringe-reduction strategy may include judicious avoidanceof emission-wavelength bands that yield the strongest fringes for agiven near-eye display configuration. Thus, in a near-eye display devicethat admits of a plurality of optical path lengths from a laser througha pupil-expansion optic, and wherein the gain profile of the lasercorresponds to a longitudinal mode spacing, the pulse width may beselected to avoid coincidence between the longitudinal mode spacing andthe plurality of optical path lengths. This can be done, for instance,by engineering a predetermined blueshift in the emission-wavelength bandof the laser. In scenarios in which coincidence between the longitudinalmode spacing and the plurality of optical path lengths gives rise to aninterference fringe, the pulse width may be increased so as to wash outthe interference fringe. In configurations including first and secondlasers of the same primary color, the pulse width of periodic modulationof the second laser may be used to wash out an interference fringecaused by emission from the first laser, or vice versa.

Generally speaking, the train of current pulses applied to the gainsection of a laser defines the average duty cycle of the laser. Computer12 may be configured to adjust the pulse separation in view of a(predetermined) pulse width, so as to control the average duty cycle.This approach can be appreciated by comparison of FIGS. 11B and 11C,where the emission-wavelength band in FIG. 11C has the same FWHM as thatof FIG. 11B but provides only half the power. The computer may controlthe average duty cycle so as to provide setpoint power in a primarycolor band, for example. The spectral broadening achievable viapulse-modulation of the drive current is also achievable viacontinuous-wave (e.g., sinusoidal) modulation with equivalent Fourierspectrum. In some examples, accordingly, the periodic current applied tothe gain section may include a radio-frequency modulated current.

FIG. 12 shows aspects of an example near-eye display method 110 to beenacted by an onboard computer of a near-eye display device. The methodis supported by the configurations herein and by other near-eye displayconfigurations.

At 112 of method 110, the computer parses a digital image. In someexamples, the digital image may correspond to a video frame. In someexamples, the digital image may be a component image representingdisplay-image content in one of a plurality of color channels. Inparsing the digital image, the computer reads a brightness valuecorresponding to coordinates X_(i), Y_(i) of each pixel i of the digitalimage.

At 114 the computer controls a matrix of electronically controllablepixel elements of an SLM of the near-eye display device. As notedhereinabove, the SLM is configured to receive emission from one or morelasers and to direct the emission in spatially modulated form to apupil-expansion optic. The matrix is controlled such that the spatiallymodulated form of the emission projects an optical image correspondingto the digital image parsed at 112. More specifically, the computergeometrically maps each pixel of the parsed digital image to a row andcolumn of the SLM and controls the bias applied to the pixel element atthe mapped row-column intersection. The bias is controlled so as toprovide the appropriate relative brightness for each locus of theoptical image emerging from the SLM.

At 116 the computer computes the average duty cycle for thepulse-modulated drive current supplied to a laser in a display projectorof the near-eye display device. The average duty cycle may be computedso as to provide color balance for field-sequential color-display whereplural lasers are pulse-modulated. In some examples the computer maycontrol the average duty cycle so as to provide setpoint power in aprimary-color band, such as a red, green, or blue band.

At 118 the computer computes a pulse width and a pulse spacing of thepulse-modulated drive current so as to operate the laser at the dutycycle computed at 116. The pulse width and pulse spacing may be computedin dependence on various factors. Such factors include (a) the averageduty cycle computed at 116, (b) the required spectral diversity, and/or(c) any of a plurality of use conditions (vide infra) of the near-eyedisplay device. In some examples the pulse width may be fully determinedby the required spectral diversity; accordingly the computer may adjustthe pulse separation in view of the fully determined pulse width, so asto arrive at the average duty cycle computed at 116.

At 120 the computer controls a drive circuit of the near-eye displaydevice to drive plural cycles of periodic current through a gainstructure of a laser while the optical image corresponding to the parseddigital image is projected. For instance, plural cycles of themodulation may be received during a period in which the SLM is set to agiven primary-color component. In this example, the periodic currentcomprises a pulse train having the pulse width and pulse spacingcomputed at 118. In some examples the periodic current includes a trainof current pulses having a pulse width of twenty nanoseconds or shorterand defining the average duty cycle.

At 122 the computer senses the total power provided within theprimary-color channel corresponding to the parsed digital image. Thepower may be sensed via a photodiode sensor arranged in a beam combinerof the near-eye display device, for example. The power sensed in thismanner may be used by the computer to iteratively refine the duty-cyclecomputation of 116, for example.

As noted above, the computer may be configured to control the averageduty cycle, pulse width, and/or pulse separation responsive to one ormore operating conditions of the near-eye display device. Generallyspeaking, the pulse width may be reduced under conditions whereincreased spectral diversity in a given color channel is required toreduce fringing and, to conserve power, increased under conditions whereincreased spectral diversity is not required. In near-eye displaydevices equipped with an eye-tracking sensor, the discriminant forwhether increased spectral diversity is required may be linked to theangle of the user's gaze within the field-of-view. In other words,angles at which problematic interference fringes do and do not appearmay be predicted based on the physical configuration of the near-eyedisplay components. The computer may be configured to apply moreaggressive fringe mitigation when the user's gaze is directed at angleswhere interference fringes are most prevalent for a given primary color.Such gaze angles may correspond to a condition in which the laser(s) ofthat primary color are driven by pulse trains of the shortest pulsewidths. In some examples, the pulse width may be shortest when thebattery is fully charged and may increase as the battery charge isdepleted. In some examples, the pulse width may be shortest under lowambient lighting, when the user is most likely to discern interferencefringes, and may increase with increasing ambient brightness. Theaverage duty cycle also may depend on the ambient light level—viz., toproject brighter display imagery under brighter ambient lighting.

In view of the various ways in which the parameters of the periodicdrive current may be controlled pursuant to changes in operatingconditions, method 110 includes, at 124, a step in which the variousoperating conditions are sensed. Such operating conditions may includebattery charge, ambient light level, and the angle of the user's gazewithin the field-of-view, as examples.

The following section provides additional non-limiting description of apupil-expansion optic 90A with reference to FIGS. 13A through 13D. Inthese drawings, optical waveguide 94 comprises a transparent (e.g.,glass or polymer) slab with a planar entry face 126 and an opposing,planar exit face 128. FIG. 13A is a plan view of entry face 126; FIG.13B is a view of exit face 128 as seen through the entry face. FIGS. 13Cand 13D are perspective views of the pupil-expansion optic rotated inopposite directions about a horizontal axis aligned to the forward edge.

Pupil-expansion optic 90 includes an entry zone 130 where the opticalimage is received through entry face 126 and an exit zone 132 where theexpanded form of the optical image is released through exit face 128.The pupil-expansion optic also includes an initial-expansion zone 134that receives the display light from entry zone 130 and expands thedisplay light en route to the exit zone. Pupil-expansion optic 90includes a plurality of differently configured diffraction gratingsarranged in the different zones.

In the illustrated example, rightward expansion grating 96R is arrangedon entry face 126, and leftward expansion grating 96L is arranged onexit face 128. The rightward and leftward expansion gratings are entrygratings that extend through initial-expansion zone 134 and overlap inentry zone 130. Exit grating 98 is arranged on entry face 126, in exitzone 132. In other examples, any, some, or all of the diffractiongratings enumerated above may be arranged on the opposite face of theoptical waveguide relative to the illustrated configuration.

Operationally, low-angle display light is received in entry zone 130,through entry face 126. Rightward expansion grating 96R and leftwardexpansion grating 96L cooperate to couple the low-angle display lightinto optical waveguide 94. Specifically, leftward expansion grating 96Ldiffracts some of the incoming, low-angle display light obliquelyrightward and downward at a supercritical angle, such that it nowpropagates through the optical waveguide in a rightward and downwarddirection. At each bounce from entry face 126, the propagating lightencounters rightward expansion grating 96R, which directs successive,increasing portions of the light directly downward. This functionexpands the display light in the rightward direction and conveys therightward-expanded display light into exit zone 132. In a complementarymanner, rightward expansion grating 96R diffracts some of the incoming,low-angle display light obliquely leftward and downward at asupercritical angle, such that it propagates through the opticalwaveguide in a leftward and downward direction. At each bounce from exitface 128, the propagating light encounters the leftward expansiongrating, which directs successive, increasing portions of the lightdirectly downward. This function expands the display light in theleftward direction and conveys the leftward-expanded display light intoexit zone 132. In the exit zone, the propagating display light at eachbounce from entry face 126 encounters exit grating 98, which directssuccessive, increasing portions of the rightward- and leftward-expandeddisplay light out of optical waveguide 94. In this manner, the displaylight is expanded in the downward direction—i.e., perpendicular to therightward and leftward expansion effected by the right- and leftwardexpansion gratings.

The following section provides additional non-limiting description ofmonocular system 18 and near-eye display device 10. Each optical imageformed by monocular system 18 is a virtual image presented at apredetermined distance Z₀ in front of user O. The distance Z₀ isreferred to as the ‘depth of the focal plane’ of the optical image. Insome monocular systems, the value of Z₀ is a fixed function of thedesign parameters of display projector 22, entry grating 96, exitgrating 98, and/or other fixed-function optics. Based on the permanentconfiguration of these structures, the focal plane may be positioned ata desired depth. In one example, Z₀ may be set to ‘infinity’, so thateach optical system presents a optical image in the form of collimatedlight rays. In another example, Z₀ may be set to 200 centimeters,requiring the optical system to present each optical image in the formof diverging light. In some examples, Z₀ may be chosen at design timeand remain unchanged for all virtual imagery presented by the displaysystem. Alternatively, the optical systems may be configured withelectronically adjustable optical power, to allow Z₀ to vary dynamicallyaccording to the range of distances over which the virtual imagery is tobe presented.

A binocular near-eye display device employing a fixed or variable focalplane may be capable of presenting virtual-display imagery perceived tolie at a controlled, variable distance in front of, or behind, the focalplane. This effect can be achieved by controlling the horizontaldisparity of each pair of corresponding pixels of the right and leftstereo images, as described below with reference to FIGS. 14A and 14B.

FIG. 14A shows right and left image frames 136R and 136L overlaid uponeach other for ease of illustration. The right image frame enclosesright optical image 20R, and the left image frame encloses left opticalimage 20L. Viewed concurrently through a near-eye display device 10, theright and left optical images may appear to the user as 3D hologram 138,comprised of individually rendered loci. Each locus i of the visiblesurface of the hologram has a depth coordinate Z_(i) associated with acorresponding pixel (X_(i), Y_(i)) of each of the right and left opticalimages. The desired depth coordinate may be simulated as follows.

At the outset, a distance Z₀ to a focal plane F of the near-eye displaysystem is chosen. Then the depth coordinate Z for every locus i of thevisible surface of the hologram is set. This is done by adjusting thepositional disparity of the two pixels corresponding to locus i in theright and left optical images relative to their respective image frames.In FIG. 14B, the pixel corresponding to locus i in the right image frameis denoted R_(i), and the corresponding pixel of the left image frame isdenoted L_(i). In FIG. 14B, the positional disparity is positive—i.e.,R_(i) is to the right of L_(i) in the overlaid image frames. Positivepositional disparity causes locus i to appear behind focal plane F. Ifthe positional disparity were negative, the locus would appear in frontof the focal plane. Finally, if the right and left optical images weresuperposed (no disparity, R_(i) and L_(i) coincident) then the locuswould appear to lie directly on the focal plane. Without tying thisdisclosure to any particular theory, the positional disparity D may berelated to Z, Z₀, and to the interpupillary distance (IPD) of the userby

$D = {{IP}D \times {( {1 - \frac{Z_{0}}{Z}} ).}}$

In some examples, computer 12 maintains a model of the Cartesian spacein front of the user, in a frame of reference fixed to near-eye displaydevice 10. The user's pupil positions are mapped onto this space, as arethe image frames 136R and 136L, each positioned at the predetermineddepth Z₀. Then, the visible surface of hologram 138 is assembled, witheach locus i of the viewable surface of the imagery having coordinatesX_(i), Y_(i), and Z_(i), in the common frame of reference. For eachlocus of the visible surface, two-line segments are constructed—a firstline segment to the pupil position of the user's right eye and a secondline segment to the pupil position of the user's left eye. The pixelR_(i) of the right optical image, which corresponds to locus i, is takento be the intersection of the first line segment in right image frame136R. Likewise, the pixel L_(i) of the left optical image is taken to bethe intersection of the second line segment in left image frame 136L.This procedure automatically provides the appropriate amount of shiftingand scaling to correctly render the visible surface, placing every locusi at the appropriate distance and with the appropriate perspective. Insome examples, the approach outlined above may be facilitated byreal-time estimation of the user's pupil positions. That variant isdescribed hereinafter, with reference to FIG. 15 . In examples in whichpupil estimation is not attempted, a suitable surrogate for the pupilposition, such as the center of rotation of the pupil position, oreyeball position, may be used instead.

Returning again to FIG. 2 , monocular system 18 may be configured tovary the focal plane on which virtual display imagery is presented. Inthe illustrated example, the monocular system includes a variable-focuslens 140 of variable optical power. Computer 12 is configured to controlthe focusing bias of the variable-focus lens such that the display lightis imaged onto a focal plane positioned at a controlled, variabledistance from pupil position 92. In stereoscopic near-eye displaydevices, this control feature may be enacted in combination withappropriate control of the stereo disparity as described above.Monocular system 18 of FIG. 2 also includes a fixed-focus lens 142 inseries with variable-focus lens 140 and arranged to pre-bias thevergence of the display light released from pupil-expansion optic 90.

Applied in an AR display system, variable-focus lens 140 and/orfixed-focus lens 142 would alter the vergence of the external lightreceived from opposite the user. In FIG. 2 , accordingly, monocularsystem 18 further comprises a variable-compensation lens 144 of variableoptical power and a fixed compensation lens 146. In some examples, thefixed optical power of fixed-compensation lens 146 may oppose andsubstantially reverse the fixed optical power of fixed-focus lens 142.When controlling the focusing bias such that the display light is imagedonto a focal plane positioned at a controlled, variable distance fromuser O, computer 12 may also synchronously control the compensation biasof the variable compensation lens such that the external light reachesthe user with unchanged vergence.

FIG. 15 is provided in order to illustrate schematically how ocularsensing may be enacted in near-eye display device 10. This approach maybe used to sense the user's pupil positions for highly accurate 3Drendering, to accommodate a range of different users, and/or to supportthe methods herein.

The configuration illustrated in FIG. 9 includes, for each monocularsystem 18, a camera 148, an on-axis lamp 150A and an off-axis lamp 150B.Each lamp may comprise a light-emitting diode (LED) or diode laser, forexample, which emits infrared (IR) or near-infrared (NIR) illuminationin a high-sensitivity wavelength band of the camera.

The terms ‘on-axis’ and ‘off-axis’ refer to the direction ofillumination of the eye with respect to the optical axis A of camera148. As shown in FIG. 15 , off-axis illumination may create a specularglint 152 that reflects from the user's cornea 154. Off-axisillumination may also be used to illuminate the eye for a ‘dark pupil’effect, where pupil 156 appears darker than the surrounding iris 158. Bycontrast, on-axis illumination from an IR or NIR source may be used tocreate a ‘bright pupil’ effect, where the pupil appears brighter thanthe surrounding iris. More specifically, IR or NIR illumination fromon-axis lamp 150A may illuminate the retroreflective tissue of theretina 160, which reflects the illumination back through the pupil,forming a bright image 162 of the pupil. Image data from the camera isconveyed to associated logic of computer 12. There, the image data maybe processed to resolve such features as one or more glints from thecornea, or the pupil outline. The locations of such features in theimage data may be used as input parameters in a model—e.g., a polynomialmodel—that relates feature position to the apparent center of the pupil.

The configuration illustrated in FIG. 15 may also be used to senserelatively long-timescale pupillary movement associated with changinggaze vector or accommodation (when enacted concurrently in the right andleft monocular systems) as well as relatively short-timescale saccadicmovement. The configuration illustrated in FIG. 15 may also be used tosense nictitation. In other configurations, the pupil position may bedetermined, estimated, or predicted in various other ways—e.g., using anelectrooculographic sensor in lieu of ocular imaging.

The methods herein may be tied to a computer system of one or morecomputing devices. Such methods and processes may be implemented as anapplication program or service, an application programming interface(API), a library, and/or other computer-program product.

FIG. 16 provides a schematic representation of a computer 12 configuredto provide some or all of the computer-system functionality disclosedherein. Computer 12 may take the form of onboard computer 12A, while insome examples at least some of the computer-system functionality may beprovided by communicatively coupled offboard computer.

Computer 12 includes a logic system 14 and a computer-memory system 16.Computer 12 may optionally include a display system 18, an input system164, a network system 166, and/or other systems not shown in thedrawings.

Logic system 14 includes one or more physical devices configured toexecute instructions. For example, the logic system may be configured toexecute instructions that are part of at least one operating system(OS), application, service, and/or other program construct. The logicsystem may include at least one hardware processor (e.g.,microprocessor, central processor, central processing unit (CPU) and/orgraphics processing unit (GPU)) configured to execute softwareinstructions. Additionally or alternatively, the logic system mayinclude at least one hardware or firmware device configured to executehardware or firmware instructions. A processor of the logic system maybe single-core or multi-core, and the instructions executed thereon maybe configured for sequential, parallel, and/or distributed processing.Individual components of the logic system optionally may be distributedamong two or more separate devices, which may be remotely located and/orconfigured for coordinated processing. Aspects of the logic system maybe virtualized and executed by remotely-accessible, networked computingdevices configured in a cloud-computing configuration.

Computer-memory system 16 includes at least one physical deviceconfigured to temporarily and/or permanently hold computer systeminformation, such as data and instructions executable by logic system14. When the computer-memory system includes two or more devices, thedevices may be collocated or remotely located. Computer-memory system 16may include at least one volatile, nonvolatile, dynamic, static,read/write, read-only, random-access, sequential-access,location-addressable, file-addressable, and/or content-addressablecomputer-memory device. Computer-memory system 16 may include at leastone removable and/or built-in computer-memory device. When the logicsystem executes instructions, the state of computer-memory system 16 maybe transformed—e.g., to hold different data.

Aspects of logic system 14 and computer-memory system 16 may beintegrated together into one or more hardware-logic components. Any suchhardware-logic component may include at least one program- orapplication-specific integrated circuit (PASIC/ASIC), program- orapplication-specific standard product (PSSP/ASSP), system-on-a-chip(SOC), or complex programmable logic device (CPLD), for example.

Logic system 14 and computer-memory system 16 may cooperate toinstantiate one or more logic machines or engines. As used herein, theterms ‘machine’ and ‘engine’ each refer collectively to a combination ofcooperating hardware, firmware, software, instructions, and/or any othercomponents that provide computer system functionality. In other words,machines and engines are never abstract ideas and always have a tangibleform. A machine or engine may be instantiated by a single computingdevice, or a machine or engine may include two or more subcomponentsinstantiated by two or more different computing devices. In someimplementations, a machine or engine includes a local component (e.g., asoftware application executed by a computer system processor)cooperating with a remote component (e.g., a cloud computing serviceprovided by a network of one or more server computer systems). Thesoftware and/or other instructions that give a particular machine orengine its functionality may optionally be saved as one or moreunexecuted modules on one or more computer-memory devices.

Machines and engines may be implemented using any suitable combinationof machine learning (ML) and artificial intelligence (AI) techniques.Non-limiting examples of techniques that may be incorporated in animplementation of one or more machines include support vector machines,multi-layer neural networks, convolutional neural networks (e.g.,spatial convolutional networks for processing images and/or video,and/or any other suitable convolutional neural network configured toconvolve and pool features across one or more temporal and/or spatialdimensions), recurrent neural networks (e.g., long short-term memorynetworks), associative memories (e.g., lookup tables, hash tables, bloomfilters, neural Turing machines and/or neural random-access memory)unsupervised spatial and/or clustering methods (e.g., nearest neighboralgorithms, topological data analysis, and/or k-means clustering),and/or graphical models (e.g., (hidden) Markov models, Markov randomfields, (hidden) conditional random fields, and/or AI knowledge bases)).

When included, display system 18 may be used to present a visualrepresentation of data held by computer-memory system 16. The visualrepresentation may take the form of a graphical user interface (GUI) insome examples. The display system may include one or more displaydevices utilizing virtually any type of technology. In someimplementations, display system may include one or more virtual-,augmented-, or mixed reality displays.

When included, input system 164 may comprise or interface with one ormore input devices. An input device may include a sensor device or auser input device. Examples of user input devices include a keyboard,mouse, or touch screen.

When included, network system 166 may be configured to communicativelycouple computer 12 with one or more other computer. The network systemmay include wired and/or wireless communication devices compatible withone or more different communication protocols. The network system may beconfigured for communication via personal-, local- and/or wide-areanetworks.

One aspect of this disclosure is directed to a near-eye display devicecomprising a pupil-expansion optic, first and second lasers, a drivecircuit coupled operatively to the first and second lasers, a beamcombiner, a spatial light modulator (SLM), and a computer. The firstlaser is configured to emit in a first wavelength band. The second laserconfigured to emit in a second wavelength band. The beam combinerconfigured to geometrically combine emission from the first and secondlasers into a collimated beam. The SLM has a matrix of electronicallycontrollable pixel elements and is configured to receive the collimatedbeam and to direct the emission in spatially modulated form to thepupil-expansion optic. Coupled operatively to the drive circuit and tothe SLM, the computer configured to: parse a digital image, trigger theemission from the first and second lasers by causing the drive circuitto drive a first current through the first laser and a second currentthrough the second laser, and control the matrix of pixel elements suchthat the spatially modulated form of the emission projects an opticalimage corresponding to the digital image.

In some implementations, the beam combiner includes one or morecollimation optics configured to collimate the emission. In someimplementations, emission from the first laser diverges maximally in afirst plane, and emission from the second laser diverges maximally in asecond plane, and the first and second lasers are oriented such that thefirst and second planes are parallel. In some implementations, the oneor more collimation optics include a first cylindrical collimation opticwith a cylindrical axis normal to the first and second planes. In someimplementations, the one or more collimation optics include a secondcylindrical collimation optic with a cylindrical axis normal to a planeorthogonal to the first and second planes. In some implementations, thebeam combiner includes a diffuser arranged optically downstream of theone or more collimation optics and configured to diffuse the emission.In some implementations, the beam combiner includes a laser despecklerarranged optically downstream of the one or more collimation optics andconfigured to despeckle the emission. In some implementations, the firstand second lasers are among a plurality of lasers coupled operatively tothe drive circuit, the beam combiner is configured to geometricallycombine emission from each of the plurality of lasers, and the pluralityof lasers includes at least one laser of each primary color. In someimplementations, a cavity of the first laser and a cavity of the secondlaser lie in a plane, and the beam combiner is configured to redirectthe emission of the first and second lasers out of the plane. In someimplementations, the beam combiner includes a mirror configured toreceive the emission of the first and second lasers. In someimplementations, the mirror supports a high-reflectance coating for eachof a plurality of primary colors. In some implementations, the mirrorand the first and second lasers are enclosed in an oxygen-depleted laserenclosure, and the laser enclosure includes a window configured totransmit the emission. In some implementations, the first and secondlasers include a shared electrode in contact with a base parallel to theplane. In some implementations, the base delimits a flat mountconfigured to carry heat away from the first and second lasers. In someimplementations, the first laser is configured to provide emission ofsubstantially higher power than the second laser. In someimplementations, the beam combiner includes one or more sensors withoutput responsive to emission of the first and/or second lasers, and thecomputer is configured to control the first and second currents furtherbased on the output. In some implementations, the digital image is oneof a plurality of component digital images parsed by the computer, eachassociated with a corresponding primary color, and the computer isfurther configured to: coordinately control the matrix of pixel elementsand the drive circuit in a time-multiplexed manner to providefield-sequential color display.

Another aspect of this disclosure is directed to a near-eye displaydevice comprising a pupil-expansion optic, first and second lasers, adrive circuit coupled operatively to the first and second lasers, a beamcombiner, an SLM, and a computer. The first laser is configured to emitin a first wavelength band. The second laser is configured to emit in asecond wavelength band. The beam combiner is configured to geometricallycombine emission from the first and second lasers into a collimatedbeam. The beam combiner includes one or more collimating optics arrangedin series with a diffuser, where the diffuser and each of the one ormore collimating optics are configured to receive the emission. The SLMhas a matrix of electronically controllable pixel elements and isconfigured to receive the collimated beam and to direct the emission inspatially modulated form to the pupil-expansion optic. Coupledoperatively to the drive circuit and to the SLM, the computer isconfigured to: parse a digital image, trigger the emission from thefirst and second lasers by causing the drive circuit to drive a firstcurrent through the first laser and a second current through the secondlaser, and control the matrix of pixel elements such that the spatiallymodulated form of the emission projects an optical image correspondingto the digital image. Here the first and second lasers are among aplurality of lasers coupled operatively to the drive circuit, the beamcombiner is configured to geometrically combine emission from each ofthe plurality of lasers, and the plurality of lasers includes at leastone laser of each primary color.

Another aspect of this disclosure is directed to a near-eye displaydevice comprising a pupil-expansion optic, first and second lasers, adrive circuit coupled operatively to the first and second lasers, a beamcombiner, an SLM, and a computer. The first laser has a first gainstructure and is configured to emit in a first wavelength band. Thesecond laser has a second gain structure and configured to emit in asecond wavelength band. The beam combiner is configured to geometricallycombine emission from the first and second lasers into a collimatedbeam. The SLM has a matrix of electronically controllable pixel elementsand is configured to receive the collimated beam and to direct theemission in spatially modulated form to the pupil-expansion optic.Coupled operatively to the drive circuit and to the SLM, the computerconfigured to: parse a digital image, trigger the emission from thefirst and second lasers by causing the drive circuit to drive a firstcurrent through the first gain structure and a periodic second currentthrough the second gain structure, and control the matrix of pixelelements such that the spatially modulated form of the emission projectsan optical image corresponding to the digital image. Here the periodicsecond current includes plural cycles of modulation driven through thesecond gain structure while the optical image is projected.

In some implementations, the beam combiner includes one or morecollimating optics arranged in series with a diffuser, the diffuser andeach of the one or more collimating optics are configured to receive theemission, the first and second lasers are among a plurality of laserscoupled operatively to the drive circuit, the beam combiner isconfigured to geometrically combine the emission from each of theplurality of lasers, and the plurality of lasers includes at least onelaser of each primary color.

It will be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific routines ormethods described herein may represent one or more of any number ofprocessing strategies. As such, various acts illustrated and/ordescribed may be performed in the sequence illustrated and/or described,in other sequences, in parallel, or omitted. Likewise, the order of theabove-described processes may be changed.

The subject matter of the present disclosure includes all novel andnon-obvious combinations and sub-combinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

1. A near-eye display device comprising: a pupil-expansion optic; afirst laser configured to emit in a first wavelength band; a secondlaser configured to emit in a second wavelength band; a drive circuitcoupled operatively to the first and second lasers; a beam combinerconfigured to geometrically combine emission from the first and secondlasers into a collimated beam; a spatial light modulator (SLM) having amatrix of electronically controllable pixel elements, the SLM beingconfigured to receive the collimated beam and to direct the emission inspatially modulated form to the pupil-expansion optic; and coupledoperatively to the drive circuit and to the SLM, a computer configuredto: parse a digital image, trigger the emission from the first andsecond lasers by causing the drive circuit to drive a first currentthrough the first laser and a second current through the second laser,and control the matrix of pixel elements such that the spatiallymodulated form of the emission projects an optical image correspondingto the digital image.
 2. The near-eye display device of claim 1 whereinthe beam combiner includes one or more collimation optics configured tocollimate the emission.
 3. The near-eye display device of claim 2wherein emission from the first laser diverges maximally in a firstplane, and emission from the second laser diverges maximally in a secondplane, and wherein the first and second lasers are oriented such thatthe first and second planes are parallel.
 4. The near-eye display deviceof claim 3 wherein the one or more collimation optics include a firstcylindrical collimation optic with a cylindrical axis normal to thefirst and second planes.
 5. The near-eye display device of claim 4wherein the one or more collimation optics include a second cylindricalcollimation optic with a cylindrical axis normal to a plane orthogonalto the first and second planes.
 6. The near-eye display device of claim4 wherein the beam combiner includes a diffuser arranged opticallydownstream of the one or more collimation optics and configured todiffuse the emission.
 7. The near-eye display device of claim 4 whereinthe beam combiner includes a laser despeckler arranged opticallydownstream of the one or more collimation optics and configured todespeckle the emission.
 8. The near-eye display device of claim 1wherein the first and second lasers are among a plurality of laserscoupled operatively to the drive circuit, wherein the beam combiner isconfigured to geometrically combine emission from each of the pluralityof lasers, and wherein the plurality of lasers includes at least onelaser of each primary color.
 9. The near-eye display device of claim 1wherein a cavity of the first laser and a cavity of the second laser liein a plane, and wherein the beam combiner is configured to redirect theemission of the first and second lasers out of the plane.
 10. Thenear-eye display device of claim 9 wherein the beam combiner includes amirror configured to receive the emission of the first and secondlasers.
 11. The near-eye display device of claim 10 wherein the mirrorsupports a high-reflectance coating for each of a plurality of primarycolors.
 12. The near-eye display device of claim 10 wherein the mirrorand the first and second lasers are enclosed in an oxygen-depleted laserenclosure, and wherein the laser enclosure includes a window configuredto transmit the emission.
 13. The near-eye display device of claim 9wherein the first and second lasers include a shared electrode incontact with a base parallel to the plane.
 14. The near-eye displaydevice of claim 13 wherein the base delimits a flat mount configured tocarry heat away from the first and second lasers.
 15. The near-eyedisplay device of claim 1 wherein the first laser is configured toprovide emission of substantially higher power than the second laser.16. The near-eye display device of claim 1 wherein the beam combinerincludes one or more sensors with output responsive to emission of thefirst and/or second lasers, and wherein the computer is configured tocontrol the first and second currents further based on the output. 17.The near-eye display device of claim 1 wherein the digital image is oneof a plurality of component digital images parsed by the computer, eachassociated with a corresponding primary color, and wherein the computeris further configured to: coordinately control the matrix of pixelelements and the drive circuit in a time-multiplexed manner to providefield-sequential color display.
 18. A near-eye display devicecomprising: a pupil-expansion optic; a first laser configured to emit ina first wavelength band; a second laser configured to emit in a secondwavelength band; a drive circuit coupled operatively to the first andsecond lasers; a beam combiner configured to geometrically combineemission from the first and second lasers into a collimated beam, thebeam combiner including one or more collimating optics arranged inseries with a diffuser, where the diffuser and each of the one or morecollimating optics are configured to receive the emission; a spatiallight modulator (SLM) having a matrix of electronically controllablepixel elements, the SLM being configured to receive the collimated beamand to direct the emission in spatially modulated form to thepupil-expansion optic; and coupled operatively to the drive circuit andto the SLM, a computer configured to: parse a digital image, trigger theemission from the first and second lasers by causing the drive circuitto drive a first current through the first laser and a second currentthrough the second laser, and control the matrix of pixel elements suchthat the spatially modulated form of the emission projects an opticalimage corresponding to the digital image, wherein the first and secondlasers are among a plurality of lasers coupled operatively to the drivecircuit, wherein the beam combiner is configured to geometricallycombine emission from each of the plurality of lasers, and wherein theplurality of lasers includes at least one laser of each primary color.19. A near-eye display device comprising: a pupil-expansion optic; afirst laser having a first gain structure and configured to emit in afirst wavelength band; a second laser having a second gain structure andconfigured to emit in a second wavelength band; a drive circuit coupledoperatively to the first and second lasers; a beam combiner configuredto geometrically combine emission from the first and second lasers intoa collimated beam; a spatial light modulator (SLM) having a matrix ofelectronically controllable pixel elements, the SLM being configured toreceive the collimated beam and to direct the emission in spatiallymodulated form to the pupil-expansion optic; and coupled operatively tothe drive circuit and to the SLM, a computer configured to: parse adigital image, trigger the emission from the first and second lasers bycausing the drive circuit to drive a first current through the firstgain structure and a periodic second current through the second gainstructure, and control the matrix of pixel elements such that thespatially modulated form of the emission projects an optical imagecorresponding to the digital image, wherein the periodic second currentincludes plural cycles of modulation driven through the second gainstructure while the optical image is projected.
 20. The near-eye displaydevice of claim 19 wherein the beam combiner includes one or morecollimating optics arranged in series with a diffuser, wherein thediffuser and each of the one or more collimating optics are configuredto receive the emission, wherein the first and second lasers are among aplurality of lasers coupled operatively to the drive circuit, whereinthe beam combiner is configured to geometrically combine the emissionfrom each of the plurality of lasers, and wherein the plurality oflasers includes at least one laser of each primary color.